Safe and efficacious dosage of flecainide acetate for treating equine atrial fibrillation

TO determine a safe and efficacious dose of flecainide acetate for treating equine atrial fibrillation (Af), the safe dosage level was determined by i njecting 1. 2, or 3 mg/kg i.v. of 1% flecainide acetate solution at a rate of 0.2 mg/kg/min to five clinically healthy horses. Clinical signs and the ECG were monitored (IIR, PR, QRS, and QT intervals) and blood was taken to measure the plasma flecainide concentration pre- and post-administration. N o abnormal signs were observed in the 1- or 2-mg/kg groups, while agitation was observed in three of five horses in the 3-mg/kg group. The QRS, and QT intervals for the 3-mg/kg group increased significantly. The peak plasma f lecainide concentrations were 1,316 +/- 358 (SD) ng/ml, 1,904 +/- 314 ng/ml , and 2,251 +/- 387 ng/ml for the 1-, 2-, and 3-mg/kg groups. respectively. To evaluate the efficacy of flecainide, Af was induced by right atrial pac ing in six clinically healthy horses, and 18 flecainide acetate solution wa s then administered until they converted to sinus rhythm. All horses with i nduced Af converted. For the conversion, a total dose of 1.40 +/- 0.63 mg/k g flecainide was required, the duration of administration was 7.00 +/- 3.15 min and plasma flecainide concentration at conversion was 1,303 +/- 566 ng /ml. In conclusion, flecainide acetate is a safe and effective antiarrhythm ic agent for equine Af, and the clinically effective dosage is 1 to 2 mg/kg .